Hi David,

I'm confused by the photo, which has a bunch of roots visible. Did you dig down around this tree? And is the root in question actually going around part of the trunk?

Here are some additional pics. Hoping this gives a better perspective. 

Hi David,

If you have the appropriate tools you can remove this root. You should try to sever it where it connects with the tree. Do so carefully so as not to damage other roots. If the connection point is too hard to find, remove the section you can see.

These pages might be helpful:

https://extension.umd.edu/resource/girdling-roots/

https://extension.psu.edu/girdling-roots-to-cut-or-not-to-cut

You’ve exposed the tree’s root flare and when you’re done you need to leave that just above the ground. A tree should not look like a telephone pole going into the ground, you should see the trunk widen at ground level.

Hope this helps. Good luck.